Hydrogen Color Code
Prerequisites
Hydrogen is colorless. The colors are labels for how it was made, and the production method determines whether hydrogen is part of the climate solution or just another way to burn fossil fuels.
Grey hydrogen: Steam methane reforming (SMR) splits natural gas (CH4) into hydrogen and CO2. Produces roughly 10 kg of CO2 per kg of H2. This is 96% of current global hydrogen production. Cost: $1-2/kg.
Blue hydrogen: Same SMR process, but CO2 is captured and stored underground. Captures 85-95% of process emissions, though upstream methane leakage from natural gas supply can erode the climate benefit. Cost: $2-3/kg.
Green hydrogen: Electrolysis powered by renewable electricity splits water into H2 and O2. Zero direct emissions if the electricity is clean. Cost: $4-8/kg.
Size the production gap. Global hydrogen production: roughly 95 million tonnes per year. Green hydrogen: less than 1% of this total. The hydrogen economy already exists; it just runs on fossil fuels.
If blue hydrogen is cheaper than green and captures most CO2, why not just use blue?
The methane leakage problem. Natural gas supply chains leak 1-3% of methane. Methane is 80x more potent than CO2 over 20 years. At leakage rates above roughly 3%, blue hydrogen's lifecycle emissions can approach grey hydrogen's. The climate benefit depends on methane leakage rates that are difficult to measure and vary widely by region.
The color taxonomy reveals that hydrogen's climate value is entirely determined by its production method.
Grey hydrogen from steam methane reforming produces ~10 kg CO2 per kg H2 and accounts for 96% of global production. This means:
Hydrogen is only as clean as its production method. Expanding fossil-based hydrogen production increases emissions. The climate case for hydrogen depends entirely on shifting production to low-carbon methods (blue with effective CCS, or green from renewables).
The answer is CLesson complete
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